Scroll of Resurrection service will provide the recipient with a free server and faction change to the inviters' own, on a single character (affected by the character from which you sent the invitation). Also, it increases their level to 80, if below. These two benefits cannot be redeemed on two separate characters.

If your friend has gone inactive before March 4, 2012 they'll most likely be eligible for the service.

Like Adréal said, you get a free server + faction change if your friend has been inactive for the last 9 months, but he lacks to mention that you also get your account upgraded to Cataclysm automatically as well, free of charge